In a wireline communication channel, where multiple signals are sent over multiple wires, the wires can be electromagnetically coupled to one another and result in an interference from one channel to another, so called near end Xtalk (NEXT) or far end Xtalk (FEXT). At the same time signals traveling in a channel can reflect back off of the imbalances in the channel and interfere with itself, so called signal echo. In most communication systems, a cancellation scheme should exist to cancel out the effect of signal echo and crosstalk from adjacent lines to achieve an acceptable bit error rate (BER), Echo and Xtalk (i.e., NEXT AND FEXT) cancellation is possible as the system has the information about the bits sent and the bits received.
The typical method to cancel the effect of echo and Xtalk in communication theory is using finite impulse response (FIR) FILTERS. The conventional method of performing echo and Xtalk cancellation using FIR filters is done fully in digital domain (other than the pre-echo cancellation for the immediate transmit pulse), where the calculated digital value of echo and Xtalk by the FIR filter is subtracted from the incoming noisy analog data input, which is digitized by an analog-to-digital conveffer (ADC).
FIG. 1 illustrates a conventional digital signal processing system 10 for a four-channel bi-directional wireline communication. In system 10 an automatic gain control (AGC) pre-echo unit 12 receives an input signal from a receiver (Rx). The signal from the pre-echo cancellation unit 12 is provided to an A/D converter 14. The digital signal from the A/D converter 14 is provided to a feed forward equalization (FFE) unit 16. The signal from the FFE unit 16 is provided to the summer 18. The output from the summer 18 is provided to slicer 20. The output of the slicer 20 is provided to a data decoder 22. The output of the slicer is also provided to an input of an Echo canceller 24 and a plurality of NEXT cancellers 26, 28,30 (for the sake of simplicity, whenever NEXT cancellers are referred to, it is meant to also include FEXT cancellers). The Echo canceller 24 receives a transmit (Tx) signal from output channel 1. The plurality of NEXT cancellers 26, 28, 30 receive Tx signals from output channels 2-4 respectively. The system can also be used to perform FEXT cancellation by a plurality of FEXT cancellers that receive as their input from the output of the slicer.
In this embodiment, the Rx signal has been distorted due to the impairments of the channel including inter-symbol interference (ISI), addition of Near End & Far End crosstalk from coupling from other transmit channels and echo of its own transmitter. The signal typically goes through the AGC to adjust signal amplitude levels, and a local echo canceller to approximately remove the immediate transmit signal, the major echo amplitude, from the received signal. System 10 requires a high resolution analog-to-digital converter (A/D 14), which translates the signal to high resolution digital information which is then equalized digitally through digital filters (possibly a Feed Forward Equalizer 16, or a Feed Back Equalizer). Furthermore, the data is detected by slicer 20 and the data error is calculated (as an example through an LMS algorithm) which in turn sets the coefficients of the appropriate FIR filter for Echo, NEXT, and FEXT cancellers. The output of the FIR filters is subtracted from the signal prior to the slicer 20. The data decoder 22 represents possible additional data decoding, which is protocol dependent, may be required to completely decode the signal for increased performance.
The typical method to cancel the effect of echo and Xtalk in communication theory is using finite impulse response (FIR) filters. The conventional method of performing echo and Xtalk cancellation using FIR filters is done fully in digital domain (other than the pre-echo cancellation for the immediate transmit pulse), where the calculated digital value of echo and Xtalk by the FIR filter is subtracted from the incoming noisy analog data input, which is digitized by an analog-to-digital converter (ADC). The digital approach, however, can have a significant complexity if the size of the FIR filters is large and thus results in large power and area on the silicon.
Accordingly, what is needed is a system and method for addressing the above-identified issues. The system and method should be cost effective, adaptable to and easily implemented existing processing systems.
The present invention addresses such a need.